Hi, don't know if anyone can help me with this. I recently purchased an 02 f-250 with a 7.3 Powerstroke. The truck has 77K on it and of course runs great. My problem is that the fuel economy has dropped significantly since I bought the pickup in February. Immediatly after I purchesed the pickup I was getting 21mpg on the highway and about 18 to 19mpg in town, which was about what I expected and I was very pleased with those milages. After having the pickup for about 3 weeks I changed the oil and air filter, replacing with sheaffers 7000 series15W-40 motor oil and the premium NAPA oil filter as well as a KNN air filter. After the service I have noticed a dramatic decrease in fuel economy. Whether the change in fuel consumption is due to the oil and filter changes I don't know, but I am getting 16mpg at the most and as low as 12mpg. I know something is wrong and it can be fixed since I had great fuel economy for a while. I wonder if something is wrong with the fuel system, I have checked for leaks and cannot find any. Can anyone shed some light on my situation. Thanks

 

I'll only tell you what I know, the 7.3 powerstroke uses engine oil to fire the injectors, so engine oil has a direct impact on operation.

 

Drop the K&N. How are you computing mileage?

 

welcome to FTE! great place to get awsome help. do you know what type of oil was use before you changed to sheaffers, parkland might be onto something. also check your Exhaust Backpressure tube and sensor for blockage.
Welcome to guzzle's Ford PSD Web Page is a great start.

 

I noticed on your profile that you're in Montana. Is that where you are now and is that where the truck is from? Altitude can have an affect on power and economy.

Were/Are you calculating fuel economy manually or using your onboard message center?

Speaking from experience, I've seen my driving habits fluctuate my fuel economy by about 4 MPG. Staying under 2k really makes a difference. Your post is showing some really strong drops in economy so there maybe something wrong. You've come to the right place to find out. The guys (and ladies) on this forum are the sharpest I've seen.

 

drop the k&n air filter and get a napa 6637 filter .

 

Welcome to FTE. Is there any reason you didn't change the fuel filter at the same time?

As asked above how are you figuring your mileage? How many miles have you put on the truck since you got it? Did the mileage drop immediately after the oil change, or was it gradual? When was the last time you filled the tank in relation to your mileage drop?

 

Welcome to FTE.

The first thing I would look at is the inter-cooler boots and make sure they are tight, then look at your up pipes and see if they are leaking. See if there is soot at the connections between the engine block and the firewall from underneath. I'd bet that it's the boots if I was a betting man.

 

sheaffers? Who makes that? JK

 

Thanks for the ideas, I will check the inter-cooler boots and drop the K&N (that was a waste of money). Honestly this is the first diesel I have owned, even though I have driven 7.3's at work quite a bit. So I am a greenhorn and not very knowledgable about the set up, but I want to learn.

I am calculating my milage manually, I do not have a message center and would not even pay attention to it if I did,I try to fill the tank slowly so it is mostly full every time I fuel up. I have put approximatly 1500 miles on the pickup since I bought it.

I took it on a 300 mile trip interstate/highway then picked up a horse trailer with three horses and towed for about 50 miles, this is where I got 20 + mpg. Then I changed the oil and returned on the same 300 mile path back home(no trailer), and this was where I noticed a strong decrease in fuel economy 16mpg and even less as the trip went on. I knew I was getting worse fuel economy just by watching the guage, there where head winds both ways so that was not a factor and should not decrease my fuel economy that much anyway. The truck currently getts 16mpg at the most right now.

I do not know what oil the previous owners were using, but when I changed it I would guess that it was 10-40 or 5-40, which would be expected since I aquired the truck in February and we have quite cold temperatures up here in the winter months. I personally would not run 15w-40 in the winter. The oil changes for the previous owner looked like they had been done at various quick lubes and I think this was the only real preventive maintainance done on the truck, I bet they rarely popped the hood, because I had to add small amounts of fluid to the rear-end, front differential, transfer case, brake fluid, grease tie-rods etc.. who knows when these things had been checked the last time. (cant get to picky when you buy used)

to the next questions (greenhorn remember)

how do I check the exaust backpressure, and how do I change the fuel filter with the pressurized system, I have done a lot of work on gas trucks so I am not completely stupid, but I do not want to hang myself by rushing into something and not knowing exactly what I am doing.

Is there a good maintainance/service manual I can buy to help me get familiar with the 7.3 psd, I dont even have an owners manual because the previous owners lost it.

Thanks to everyone for the help!